The present invention relates to a solid state image sensing device, and in particular, to a solid state image sensing device that has an effective pixel region for detecting optical information of a subject and an ineffective pixel region for detecting optical black.
In general, as shown in FIG. 6, a CCD (charge coupled device) area sensor has an effective pixel region A for detecting optical information of a subject and an ineffective pixel region B for detecting optical black. Further, the ineffective pixel region B is normally provided on the right and left sides and upper and lower sides of the effective pixel region A.
FIG. 7 shows a sectional view of the effective pixel region A (corresponding to a cross section in an inner portion of the arrow line C-Cxe2x80x2 in FIG. 6) in a conventional CCD area sensor. FIG. 8 shows a sectional view of the ineffective pixel region B (corresponding to the cross section in an outer portion of the arrow line C-Cxe2x80x2 in FIG. 6). Pixel constructions of the effective and ineffective pixel regions in the conventional CCD area sensor are described below with reference to FIGS. 7 and 8.
As shown in FIG. 7, the effective pixel region A has a pixel construction such that a light-receiving region 3, a transfer channel region 4 and a read region 5 for transferring electric charges generated by photoelectric conversion in the light-receiving region 3 to the transfer channel region 4 are formed in a p-type impurity region 2 formed on an n-type silicon substrate 1. On top of the transfer channel region 4 and the read section 5, a transfer electrode 8 of a polysilicon film doped with phosphorus is selectively formed with interposition of a silicon oxide film 6 and a silicon nitride film 7.
Then, an insulating film 9 is formed of, for example, a silicon oxide film by CVD (chemical vapor deposition) on the entire surface including the transfer electrode 8. Further, a high-melting point metal 10 of, for example, TiW is selectively formed as a light shielding film so as to cover the region of the transfer electrode 8. A BPSG (boro-phospho silicate glass) film 11 is further formed on the entire surface including the high-melting point metal 10, and an wiring metal 12 of, for example, Alxe2x80x94Si is formed on this BPSG film 11 and thereafter selectively removed (the wiring metal 12 is removed in FIG. 7) . Then, a surface protecting film 13 of, for example, a SiN film is formed by plasma CVD on the entire surface of the wiring metal 12.
On the other hand, as shown in FIG. 8 where the components corresponding to FIG. 7 are denoted by the same reference numerals, the pixel construction of the ineffective pixel region B is roughly equal to the pixel construction of the effective pixel region A. It is to be noted that the light-receiving region 3 is covered with the high-melting point metal 10 and the entire surface is covered with the wiring metal 12 in order to prevent light from entering the light-receiving region 3, dissimilar to the effective pixel region A.
However, the aforementioned conventional CCD area sensor has the disadvantages as follows. In general, hydrogen annealing is performed through the fabricating processes of the CCD area sensor. The hydrogen annealing has the effects of reducing the interface state densities of the light-receiving region 3 and the transfer channel region 4 and reducing a dark-time output voltage. Particularly in the effective pixel region A, the surface protecting film 13 contains a large amount of hydrogen, and the large amount of hydrogen is diffused from the surface protecting film 13 toward the silicon substrate 1. Therefore, the dark-time output voltage can be sufficiently reduced.
In the ineffective pixel region B, however, the high-melting point metal 10 and the wiring metal 12 are laminated on top of the light-receiving region 3. Therefore, the diffusion of hydrogen ions from the surface protecting film 13 constructed of an SiN film toward the silicon substrate 1 is not sufficiently effected, for which the dark-time output voltage is not reduced to such an extent as in the effective pixel region A.
For the above-mentioned reasons, there occurs a difference between the effective pixel region A and the ineffective pixel region B in terms of the black level. Then, signal processing is executed on the basis of the black level of the ineffective pixel region B used as a reference. Therefore, the signal processing is executed in a state in which the black at the reference level is shifted to the white side with respect to the black at the proper reference level, and this causes a disadvantage in gray scale accuracy.
Accordingly, an object of the present invention is to provide a solid state image sensing device that has no difference between the effective pixel region and the ineffective pixel region in terms of the black level.
In order to achieve the above-mentioned object, the present invention provides a solid state image sensing device that has a light-receiving section, a transfer channel section and a read section on an identical substrate and is separated into an effective pixel region for detecting optical information of a subject and an ineffective pixel region for detecting optical black, the device comprising: a first light shielding film that covers the transfer channel section and the read section in the effective pixel region and the ineffective pixel region and is arranged so as to provide an opening on the light-receiving section; an interlayer insulating film that is formed on the first light shielding film and the light-receiving section in the effective pixel region and the ineffective pixel region; a second light shielding film that is formed on the interlayer insulating film in at least the ineffective pixel region and is arranged so as to cover the light-receiving section, the transfer channel section and the read section in at least the ineffective pixel region; and a protective insulating film that is formed on the interlayer insulating film and the second light shielding film to cover their entire surface in the effective pixel region and the ineffective pixel region.
According to the above construction, the first light shielding film formed on the transfer channel section and the read section in the ineffective pixel region has an opening on the light-receiving section. Therefore, in the ineffective pixel region, if the second light shielding film that is arranged on the first light shielding film and covers the light-receiving section, the transfer channel section and the read section is formed of the material that is easy for hydrogen ions to penetrate, then the diffusion of hydrogen ions from the protective insulating film toward the substrate is sufficiently effected in the ineffective pixel region in the hydrogen annealing stage even though the first light shielding film is made of a material that is hard for hydrogen ions to penetrate, by which the interface state densities of the light-receiving section and the transfer channel section are reduced. As a result, the black level of the ineffective pixel region similarly becomes equivalent to the black level of the effective pixel region that has an opening on the light-receiving section of the first light shielding film, causing no difference.
The present invention also provides a solid state image sensing device that has a light-receiving section, a transfer channel section and a read section on an identical substrate and is separated into an effective pixel region for detecting optical information of a subject and an ineffective pixel region for detecting optical black, the device comprising: a first light shielding film that covers the transfer channel section and the read section in the effective pixel region and the ineffective pixel region and is arranged so as to provide an opening on the light-receiving section; an interlayer insulating film formed on the first light shielding film and the light-receiving section in the effective pixel region and the ineffective pixel region; a second light shielding film that is formed on the interlayer insulating film in at least the ineffective pixel region and is arranged so as to cover the light-receiving section and provide an opening in a region other than the light-receiving section; and a protective insulating film that is formed on the interlayer insulating film and the second light shielding film to cover their entire surface in the effective pixel region and the ineffective pixel region.
According to the above construction, the first light shielding film formed on the transfer channel section and the read section has an opening on the light-receiving section in the ineffective pixel region. Furthermore, the second light shielding film located on the first light shielding film covers the light-receiving section and has an opening in a region other than the light-receiving section in the ineffective pixel region. Therefore, even though the first light shielding film is made of a material that is hard for hydrogen ions to penetrate and the second light shielding film is made of a material that is hard for hydrogen ions to penetrate, then the diffusion of hydrogen ions from the protective insulating film toward the substrate is sufficiently effected in the ineffective pixel region in the hydrogen annealing stage because of the openings. As a result, the interface state densities of the light-receiving section and the transfer channel section are reduced.
In one embodiment of the invention, the second light shielding film is made of a metal film for wiring use.
According to the above construction, the wiring metal film functions as a second light shielding film. Accordingly, there is no need for providing the second light shielding film in addition to the first light shielding film, and this allows the reduction in thickness and cost of the solid state image sensing device.
In one embodiment of the invention, the metal film for wiring use is formed of a material that blocks penetration of hydrogen.
In one embodiment of the invention, the metal film for wiring use is formed of a laminate structure film that includes Ti or a Ti alloy.
According to the above construction, even though the wiring metal film is formed of the multi-layer structure film of the barrier metal that includes Ti or a Ti alloy and the reflection preventing film for the achievement of finer pixels, then the diffusion of hydrogen ions is sufficiently effected in the ineffective pixel region in the hydrogen annealing stage. As a result, the interface state densities of the light-receiving section and the transfer channel section are reduced.